Merge pull request microsoft#41075 from uhyo/fix-36958

allow type narrowing with NonNullExpression

Author: weswigham

src/compiler/binder.ts

@@ -845,7 +845,8 @@ namespace ts {
                 case SyntaxKind.CallExpression:
                     return hasNarrowableArgument(<CallExpression>expr);
                 case SyntaxKind.ParenthesizedExpression:
-                    return isNarrowingExpression((<ParenthesizedExpression>expr).expression);
+                case SyntaxKind.NonNullExpression:
+                    return isNarrowingExpression((<ParenthesizedExpression | NonNullExpression>expr).expression);
                 case SyntaxKind.BinaryExpression:
                     return isNarrowingBinaryExpression(<BinaryExpression>expr);
                 case SyntaxKind.PrefixUnaryExpression:

src/compiler/checker.ts

@@ -22618,7 +22618,8 @@ namespace ts {
                     case SyntaxKind.CallExpression:
                         return narrowTypeByCallExpression(type, <CallExpression>expr, assumeTrue);
                     case SyntaxKind.ParenthesizedExpression:
-                        return narrowType(type, (<ParenthesizedExpression>expr).expression, assumeTrue);
+                    case SyntaxKind.NonNullExpression:
+                        return narrowType(type, (<ParenthesizedExpression | NonNullExpression>expr).expression, assumeTrue);
                     case SyntaxKind.BinaryExpression:
                         return narrowTypeByBinaryExpression(type, <BinaryExpression>expr, assumeTrue);
                     case SyntaxKind.PrefixUnaryExpression:

tests/baselines/reference/narrowingWithNonNullExpression.js

@@ -0,0 +1,10 @@
+//// [narrowingWithNonNullExpression.ts]
+const m = ''.match('');
+m! && m[0];
+m?.[0]! && m[0];
+
+
+//// [narrowingWithNonNullExpression.js]
+var m = ''.match('');
+m && m[0];
+(m === null || m === void 0 ? void 0 : m[0]) && m[0];

tests/baselines/reference/narrowingWithNonNullExpression.symbols

@@ -0,0 +1,14 @@
+=== tests/cases/compiler/narrowingWithNonNullExpression.ts ===
+const m = ''.match('');
+>m : Symbol(m, Decl(narrowingWithNonNullExpression.ts, 0, 5))
+>''.match : Symbol(String.match, Decl(lib.es5.d.ts, --, --))
+>match : Symbol(String.match, Decl(lib.es5.d.ts, --, --))
+
+m! && m[0];
+>m : Symbol(m, Decl(narrowingWithNonNullExpression.ts, 0, 5))
+>m : Symbol(m, Decl(narrowingWithNonNullExpression.ts, 0, 5))
+
+m?.[0]! && m[0];
+>m : Symbol(m, Decl(narrowingWithNonNullExpression.ts, 0, 5))
+>m : Symbol(m, Decl(narrowingWithNonNullExpression.ts, 0, 5))
+

tests/baselines/reference/narrowingWithNonNullExpression.types

@@ -0,0 +1,27 @@
+=== tests/cases/compiler/narrowingWithNonNullExpression.ts ===
+const m = ''.match('');
+>m : RegExpMatchArray
+>''.match('') : RegExpMatchArray
+>''.match : (regexp: string | RegExp) => RegExpMatchArray
+>'' : ""
+>match : (regexp: string | RegExp) => RegExpMatchArray
+>'' : ""
+
+m! && m[0];
+>m! && m[0] : string
+>m! : RegExpMatchArray
+>m : RegExpMatchArray
+>m[0] : string
+>m : RegExpMatchArray
+>0 : 0
+
+m?.[0]! && m[0];
+>m?.[0]! && m[0] : string
+>m?.[0]! : string
+>m?.[0] : string
+>m : RegExpMatchArray
+>0 : 0
+>m[0] : string
+>m : RegExpMatchArray
+>0 : 0
+

tests/cases/compiler/narrowingWithNonNullExpression.ts

@@ -0,0 +1,3 @@
+const m = ''.match('');
+m! && m[0];
+m?.[0]! && m[0];